Checking lbw stability, rfi sep10

• 27sep10: 300 second test covering all of lband using the mock spectrometer
• 29sep10: 4200 second test using the interim correlator and the setup of a2335 (who originally reported the problem).
  

27sep10: 300 second integration over entire band:

• The mock spectrometer was used to cover the entire band.
• 4 bands of 172 MHz bandwidth and 8192 channels (20KHz resolution) were used.
• The cfr for the bands were: 1200,1350,1500,and 1650 MHz.
• 3000 .1 second integrations were taken.
• The telescope sat at az=285, za=9 degrees.
• The data was taken around 17:00 ast. There was  some lightening in the distance.
  

Processing the data:

• dynamic spectra were made for each band (polB)
• the average spectra was computed for each band.
• the rms/mean by channel was computed for each band.
• An rfi mask was generated by finding all rms/mean channels larger than 3 sigma
• The rfi mask was used to compute the total power for each band.

Data plots,images:

• PolB images of the 3 bands
• each spectra has been normalized to the median spectrum to flatten the image.
  
• Since the telescope was stationary, continuum sources drift through the beam.
• The vertical scale is seconds (with .1 sec resolution)
• I've  labeled some of the more obvious rfi.
  
• 1200 MHz dynamic spectra (.gif)
• the 4 radars 1232-1256 are from punta salinas. You can see their blanking when they point at us.
  
• 1227 is gps l2 (with low level spread).
• 1248 : low level rfi is glonass.
  
• 1350 MHz dynamic spectra (.gif)
• 1330,1350 radar is faa.
• 1370 radar is 1330 mixer image.
  
• 1290 radar: punta borinquen
• 1410 is mixer image.
• narrow in time, horizontal lines (28,90,..) are lightening
• 
  
• 1500 MHz dynamic spectra (.gif)
• 1525-1550 inmarsat sat to ground
• 1575 and associated low level rfi.. gps L1
  
• 1650 MHz dynamic spectra (.gif)
• 1575 gps L1
• 1598-1608 - glonass satellites
• 1618-1628 - iridium

• 5 minute average spectra and  rms/mean (.ps) (.pdf)
• top: 5 minute average
• bottom: rms/mean by channel
• The green line is the expected rms/mean from the radiometer equation.
  
• The rms/mean is greater than the expected value because of the continuum sources.
• The dc channel birdie is not stable (since it's rms is larger).
• Some of the rms/mean rfi is polarized.. 1302,1303,
  
• total power vs time (.ps) (.pdf)
• the rfi was excluded from the total power accumulation.
  
• top: total power vs time polA, polB
• bottom: TotalPwrA/totalPwrB vs time
• You can see the compression every 12 seconds from the radars.
• There is no large drifting as seen back in jul10.
  

29sep10: 4200 second test around 1385 MHz.

• lband wide, linear mode, 1280 hipass filter and 1230-1470 filter in place
• telescope sitting at 272 and 8 degrees za
• interim correlator 9 level sampling, 1 second spectra, 25 Mhz bw, 1024, centered at 1385.
• take data for 4200 seconds.

    Processing the data:

• rms/mean computed over the 4200 seconds and then a mask was created using a linear fit to rms/mean.
• total power was computed using the above mask.
• the spectrum of the total power was also computed.

• page 1 top: total power vs RA.
• black is polb, red is polb.
  
• the horizontal scale shows how the sky drifted by for the 4200 seconds.
• page 1 bottom: ratio pola/polb vs time
• horizontal scale is not in secondsl
• You see variations in the ratio at the beginning.
• the variations are probably coming from the sky.
  
• The telescope was pointing close to the north polar spur which is polarized.
• Page 2 top: spectrum of total power.
• black is polA, red is polB. polB has been offset for display.
• The max freq is .5 hz (from the 1 second sampling).
• polA seems to have more variation in the .1 to .3 hz region than polb.
• the green line at .2 Hz would be the alias of the 1.2 hz crosshead frequency. nothing is seen.
  
• Page 2 bottom: blowup of horizontal scale.
• On this scale both pols look the same.

    Summary:

• no large drifts or jumps are seen.
• polA looks looks a little noiser in the .1 to .3 hz range.
• there is no power variation at the crosshead frequency